Compositions and methods for prevention of photoaging

ABSTRACT

Methods of preventing photoaging and sun burn by topically applying a composition containing caffeine or a compound structurally similar to caffeine are provided. Pharmaceutical compositions comprising caffeine or a compound structurally similar to caffeine for the prevention of photoaging and sun burn are also provided.

BACKGROUND OF THE INVENTION

The effects of ultraviolet radiation from exposure to the sun on humanskin are a growing concern for today's longer-lived population. Themajority of changes associated with an aged appearance result fromchronic sun-damage (Warren et al., J. Am. Acad. Dermatol., 1991,25:751-760; Frances, C. and Robert, L., Int. J. Dermatol., 1984,23:166-179). Dramatic alterations of the superficial dermis accompanythe deep wrinkles and laxity common in photoaged skin. The majorhistopathologic alteration of photoaged skin is the accumulation ofmaterial which, on routine histopathologic examination, has the stainingcharacteristics of elastin and is, thus, termed solar elastosis.Immunohistochemical staining has shown the poorly-formed fiberscomprising solar elastosis to be composed of elastin (Chen et al., J.Invest. Dermatol., 1986, 87:334-337; Mera et al., Br. J. Dermatol.,1987, 117:21-27) fibrillin (Chen et al., J. Invest. Dermatol., 1986,87:334-337; Dahlback et al., J. Invest. Dermatol., 1990, 94:284-291;Bernstein et al., J. Invest. Dermatol., 1994, 103:182-186) and versican,the normal components of elastic fibers (Zimmerman et al., J. Cell.Biol., 1994, 124:817-825). A coordinate increase in elastin, fibrillinand versican mRNAs has been demonstrated in fibroblasts derived fromphotodamaged skin, as compared to fibroblasts derived from normal skinfrom the same individuals (Bernstein et al., J. Invest. Dermatol., 1994,103:182-186). Elevated elastin mRNA levels in sun-damaged skin resultfrom enhanced elastin promoter activity, as shown by transienttransfections of fibroblasts with a DNA construct composed of the humanelastin promoter linked to the chloramphenicol acetyltransferase (CAT)reporter gene (Bernstein et al., J. Invest. Dermatol., 1994,103:182-186).

It has now believed that topical application of a composition comprisingcaffeine or a structurally related compound prevents photoaging andother skin damage resulting from exposure to solar, and morespecifically, ultraviolet radiation.

SUMMARY OF THE INVENTION

In the present invention, a new use is provided for compositionscomprising caffeine or structurally related compounds. It is nowbelieved that topical application of caffeine or a structurally relatedcompound will provide protection against photoaging and other sun-damagesuch as sunburn caused by solar radiation. Accordingly, caffeine andcompounds structurally similar to caffeine are believed to be useful assunscreen agents. Compositions for use as sunscreen agents comprisingcaffeine or a compound structurally similar to caffeine are alsoprovided.

DETAILED DESCRIPTION OF THE INVENTION

Profound changes take place in the superficial dermis as a result ofchronic sun-exposure. The major alteration is the deposition of massiveamounts of abnormal elastic material, termed solar elastosis. It hasbeen shown that solar elastosis is accompanied by elevations in elastinand fibrillin mRNAs and elastin promoter activity.

A transgenic mouse model which contains the human elastin promoterlinked to a chloramphenicol acetyltransferase (CAT) reporter gene fortesting compounds that may inhibit cutaneous photodamage has beendeveloped. These mice express human elastin promoter activity in atissue-specific and developmentally regulated manner. Promoter activitycan be studied in this model as a function of small increases inultraviolet radiation, demonstrating the sensitivity of the assay. Inaddition, quantitative data can be obtained after only a single exposureto ultraviolet radiation. A test compound is applied to the skin of atransgenic mouse capable of expressing the human elastin promoter. Thetransgenic mouse is then exposed to solar radiation and human elastinpromoter activity in the mouse is determined. The human elastin promoteractivity is then compared to that in transgenic mice also exposed to anequivalent dose of solar radiation which were not treated with the testcompound to determine whether or not the test compound providedprotection against the solar radiation. Since elastin promoteractivation is a primary event in cutaneous aging, these mice represent amouse model of human photoaging.

Using this transgenic mouse line, the ability of caffeine and compoundsstructurally similar to caffeine to inhibit the effects of solarradiation on human elastin promoter activity can be determined. In theseexperiments, mice will be divided into three groups, one group receivingno treatment, one group wherein a solution or suspension of caffeine ora compound structurally similar to caffeine in a pharmaceuticallyacceptable vehicle for topical application is applied topically to theirbacks, and a third group wherein the pharmaceutically acceptable vehiclealone is applied topically to their backs. Approximately fifteen minutesafter topical application, the mice are exposed to 20 human minimalerythema doses (MEDs) of solar simulating radiation (SSR). Followingphototreatment, the backs of the mice are rinsed twice with 70%isopropyl alcohol pads to remove any excess caffeine or compoundstructurally similar to caffeine. This procedure is repeated over threeconsecutive days.

Mice are then sacrificed and skin harvested for determination of CATactivity 24 hours after the third phototreatment. The baseline CATactivity of control mice receiving neither radiation nor treatment isstandardized to a value of one. Relative increases in CAT activity inmice treated with vehicle alone are then compared with CAT activity inmice treated with vehicle containing caffeine or a compound structurallysimilar to caffeine.

Results of these experiments are expected to demonstrate that topicalapplication of a composition comprising caffeine or a compoundstructurally related thereto to the skin provides protection againstphotoaging and other sun-damage such as sunburn. By “compoundstructurally similar to caffeine”, it is meant it is meant a compoundwith a similar chemical formula and structure which exhibits similarphotodamage protective properties to caffeine. Examples include, but arenot limited to, additional xanthines such as methylated xanthinestheophylline and theobromine. Methods of rationally designing additionalchemical compounds with similar structure to a known compound are wellestablished and used routinely by those of skill in the art.Accordingly, upon reading of the instant application, structurallysimilar compounds to caffeine and other methylxanthines such astheophylline and theobromine for use in the present invention can beidentified routinely by those of skill in the art.

Examples of compositions comprising caffeine or a structurally similarcompound to caffeine include, but are not limited to creams, lotions andsprays. Methods of formulating caffeine of structurally similar compoundto caffeine into creams, lotions and sprays as well as pharmaceuticaladditives for such formulations are well known to those skilled in theart. As will be obvious to those skilled in the art upon thisdisclosure, such compositions may further comprise secondary oradditional sunscreens or free radical scavengers such as, but notlimited to, Vitamin C and Vitamin E and analogs thereof. In a preferredembodiment, a composition comprising caffeine or a structurally similarcompound to caffeine is applied to the skin prior to exposure to thesun. However, application of these compositions subsequent to theexposure can also mitigate any damage resulting to the skin from thisexposure. It is believed that these compositions of the presentinvention will be especially useful in protecting individuals withheightened sensitivities to the sun, such as, but not limited to,individuals undergoing psoralen treatment for cancer, psoriasis andother skin conditions; individuals undergoing photodynamic therapy forskin cancer, psoriasis and other skin conditions; individuals sufferingfrom genetic repair defects such as xeroderma pigmentosa, albinism orother conditions resulting from decreased endogenous melanin pigment.

The following nonlimiting examples are provided to further illustratethe present invention.

EXAMPLES Example 1 Transgenic Mice Expressing the Human Elastin Promoter

A homozygous line of transgenic mice expressing the 5.2-kb human elastinpromoter linked to a CAT reporter gene is used. Hsu-Wong et al., J.Biol. Chem., 1994, 269:18072-18075. These mice express the human elastinpromoter in a tissue-specific and developmentally regulated manner. Micefour or five days old were used since at this age, visible hair growthis not yet present.

Example 2 Solar Simulating Radiation

A Multiport Solar Simulator (Solar Light Company, Philadelphia, Pa.)containing a xenon arc lamp filtered through a Schott WG 320 filter(Schott Glaswerke, Mainz, Germany) can be used to administer solarsimulating radiation (SSR). The output of the solar simulator ismeasured by means of a 3D UV meter (Solar Light Company) and displayedas human minimal erythema doses (MEDs). The emission spectrum of thelamp closely simulates solar radiation reaching the earth's surface. Thelight guides from the solar simulator are placed in light contact withthe dorsal surface of the mice, which are restrained to prevent movementwhile SSR is administered.

Unirradiated control mice are also restrained without receiving SSR.

Example 3 CAT Assay

To measure the expression of the human elastin promoter/CAT reportergene construct in the skin of transgenic mice and in fibroblast culturesestablished from these animals, CAT activity is determined. Forextraction of the CAT from skin, the specimens are homogenized in 0.25Tris-HCl, OH 7.5, using a tissue homogenizer (Brinkmann Instruments,Inc. Westbury, NY). The homogenates are centrifuged at 10,000 ×g for 15minutes at 4° C. and the protein concentration in the supernatantdetermined by a commercial protein assay kit (Bio-Rad Laboratories,Richmond, Calif.). Aliquots of the supernatant containing 100 μg ofprotein are used for assay of CAT activity by incubation with [⁴C]chloramphenicol in accordance with well-known procedures. The acetylatedand non-acetylated forms of radioactive chloramphenicol are separated bythin-layer chromatography and CAT activity is determined by theradioactivity in the acetylated forms as a percent of the totalradioactivity in each sample.

1. A method of protecting humans exposed to sunlight against photoagingand sunburn comprising-topically applying to skin of a human acomposition comprising caffeine or a compound structurally similar tocaffeine in an amount effective to protect the skin against photoagingand sunburn.
 2. The method of claim 1 wherein the composition comprisescaffeine, theophylline or theobromine.
 3. The method of claim 1 whereinthe composition is applied prior to exposure of the skin to sunlight. 4.The method of claim 1 wherein the composition is applied subsequent toexposure of the skin to sunlight.
 5. A method of protecting individualswith a heightened sensitivity to the sun from damage resulting from thesun comprising topically applying to the skin of an individual with aheightened sensitivity to the sun a composition comprising caffeine or acompound structurally similar to caffeine prior to exposure of theindividual to the sun.
 6. The method of claim 5 wherein the compositioncomprises caffeine, theophylline or theobromine.
 7. A pharmaceuticalcomposition for prevention of photoaging and sunburn comprising caffeineor a compound structurally similar to caffeine and a second sunscreen orfree radical scavenger.